Heretofore, there has been proposed an automatic range finder associated with an automatic focussing camera, wherein by using the principle of triangulation, two optical systems are spaced a given base length apart from each other, one of which serves as a light projecting system and the other of which serves as a light receiving system, and the light projected through the light projecting system to an object of the range finding is led through the light receiving system to one of a plurality of light receiving elements provided in the light receiving system, whereby the distance to the object of the range finding is measured.
The principle of such a range finder is shown in FIG. 1, wherein 2 denotes a light source; 4 denotes a lens in the light projecting system; 6 denotes a lens in a light receiving system spaced a base length l apart from the lens 4 in the light projecting system; 8a, 8b, 8c and 8d denote light receiving elements disposed rearwardly of the lens 6 in the light receiving system; and 10 denotes a detector having the inputs of said light receiving elements 8a, 8b, 8c and 8d separately inputted thereto for finding the distance to an object of the range finding by means of the output from such light receiving element. The respective positions of the light receiving elements are such that if a subject (an object of range finding) is located at a position a, the light receiving element 8a alone receives the reflected light which originates from the light source 2; similarly, if it is located at a position b, the light receiving element 8b alone receives the reflected light; if it is located at a position c, the light receiving element 8c alone receives the reflected light; and if it is located at a position d, the light receiving element 8d alone receives the reflected light. The detector 10 determines the distance to the object of range finding by reason of the fact that the output from the particular light receiving element which receives the light projected by the light source 2 and reflected from the object of range finding increases.
In the automatic range finder of the triangulation type described above, in order to increase accuracy, it may be contemplated to increase the base length l or decrease the divergence of the flux of light projected to the object of range finding. However, in devices limited in space, such as cameras, since it is preferable that the base length l be as small as possible, it is necessary to decrease the divergence of flux of light projected to the object of range finding. Thus, it has been proposed to use a light emitting diode of a PN junction as a light source for the range finder so that the narrow intense light emitted from the lateral plane perpendicular to the PN junction (the light being hereinafter referred to as the lateral plane light) is used as light to be projected to an object of range finding.
An example of a range finder using the lateral plane light from a light emitting of a PN junction is shown in FIG. 7 (b) of Japanese Patent Laid Open Publication No. 54-40662 (laid open on Mar. 30, 1979). The device shown in the figure comprises a plurality of light receiving elements secured to and wire-bonded to a base plate which is disposed parallel to the base length for triangulation and is provided at an end thereof with a light emitting diode mounting recess, and a light emitting diode chip die-bonded in the recess so that it emits light substantially parallel to the base plate, the chip being wire-bonded to the base plate.
However, since the surface of the base plate of the above described range finder has light receiving elements and an IC attached thereto, the die bonding and wire bonding of the light emitting diode chip to the end of the base plate subsequent to the bonding of the light receiving elements and the IC involve difficulties in holding the base plate and in applying heat necessary for bonding and also entail a danger of breaking the bonding wire. Moreover, the wire remains exposed at the end of the base plate after the bonding of the light emitting diode chip, so that there is a danger that the wire is broken during the handling of the base plate.